Casting cores are conventionally prepared by machinery such as is described in commonly owned Japanese examined utility model publication (Kokoku) No. Heisei 5-30833 and in Japanese unexamined patent publication (Kokai) No. Heisel 5-305386. In the proposed conventional machinery a mold sand feeder tank includes a mold sand tank portion filled with mold sand and an air supply and discharge chamber which supplies pressurized air to the lower portion of the mold sand feeder tank through metal wire mesh and applies suction. The mold sand filling the mold sand tank portion is fed into a hollow core molding portion formed by clamping together a pair of divided mold portions. The mold sand is fed into the hollow portion where it contacts with the wall surface of the core fabrication apparatus and is heated and becomes hardened. This is, because the sand is coated with a thermosetting resin. This coated sand is referred to in the specification with its claims as "mold sand."
Subsequently suction is applied to the hollow core molding portion through the mold sand in the mold sand tank portion and through a gap of the mold sand by switching into air exhausting from the air supply and discharge chamber. The unheated, non-hardened, loose mold sand in the center portion of the hollow core molding portion is collected in the same mold sand tank.
In the aforementioned conventional machine, while the mold sand is fed from the mold sand tank portion of the mold sand feeding tank to the hollow core molding portion to heat and harden the mold sand in the center portion, the pressurized air in the air supply and discharge chamber has to be constantly supplied toward the hollow core molding portion so that the mold sand will not leak by flowing from the hollow core molding portion to the mold sand tank portion.
On the other hand, when the non-hardened mold sand is recovered into the mold sand tank after hardening of the mold sand by heating it in the hollow core molding portion, the suction is applied to the hollow core molding portion through the mold sand filled in the mold sand tank portion and through a gap of the mold sand, by switching to exhausting air from the air supply and discharge chamber located below the mold sand tank portion. Therefore, the mold sand interferes with the action of the suction and results in delay and lowers the mold sand correcting efficiency. Due to the low suction, vibration action is applied to recover the non-hardened mold sand in the hollow core molding portion to release the non-hardened sand from the wall surface of the hollow core molding portion for its recovery. This is a source of unwanted noise in the workplace.
On the other hand, undesired semi-hardened or hardened mold sand can be recovered into the mold sand tank portion together with the non-hardened mold sand with the mold sand hardened by heating by contact with the wall surface of the hollow core molding portion. The non-hardened mold sand recovered into the mold sand tank portion is again fed into the hollow core molding portion. When the mold sand is fed into the hollow core molding portion together with semi-hardened mold sand and the hardened mold sand, the firm hollow core cannot be formed. The wall of the hollow core becomes broken away and makes it impossible to mold the core.